With the tremendous growth of data processing, local area networks and wide area networks have evolved as a way to permit digital communications among various devices, such as server devices for one or more data terminals (DTEs), computers, etc. As illustrated in FIG. 1, local area networks (LANs) 10 utilize a medium 12 to interconnect any number of nodes 14, the latter being a term used to represent the various devices digitally connected together through the medium 12. While the nodes 14 can represent the same or different devices, all of the nodes 14 communicate via the LAN medium 12 in accordance with a packet-type protocol with data therefore being transmitted in individual packets. Many protocols have been developed, the most notable are the Ethernet (IEEE 802.3 10base2, 10base5, or 10baseT) type or the Token Ring (IEEE 802.5 4Mbps or 16Mbps) type.
Occasionally, it is necessary or desirable for nodes 14 to communicate with other nodes not directly connected to the LAN medium 12. One system which has been developed to accomplish this task is the wide area network (WAN) 20 which utilizes a bridge/router 16 between it and each of the local area networks 10 to which it is connected. The bridge/router 16 is placed between the WAN 20 and the LAN via a digital link 18. Data is usually compressed in each remote bridge/router 16 before it is placed on the digital link 18 and processed by the WAN, and decompressed by the bridge/router 16 when compressed data is received over the digital link 12 from the WAN 20.
More specifically, as shown in FIG. 2, generally data from the LAN medium 12 is translated through a Media Access Unit (MAU) 22 to a form appropriate for data and clock recovery by the LAN interface 24 in the remote bridge/router 16. The data is transmitted in packets. If the packet of information from the LAN interface 24 is to be passed over the WAN link 18 to a remotely attached companion bridge/router, then it will be placed in shared memory and made available to the WAN interface 28 through the host processor platform 26. The host processor platform 26 of the typical currently available bridge/routers includes at least one data processor for performing the data compression or decompression and a microprocessor containing the necessary programs for compressing or decompressing data. Data compression enables more data to be transmitted through the data link 18 at a particular rate of transmission than uncompressed or raw data at its clocked data rate. The decompression of the data is typically performed in a complementary fashion from the compression technique so that the decompressed data should be identical to the initial raw data. One standard bridge/router is the MLB 6000 manufactured and sold by Microcom, Inc., of Norwood, Mass., the present assignee. The latter bridge/router is very effective in accomplishing its tasks. However, the Microcom bridge/router, which utilizes a high speed microprocessor incorporating software based compression and decompression programs, is only capable of compressing data which is transmitted at a rate of 64 Kbps or less. Should data be transmitted into the bridge/router at a greater rate, the device is adapted to disable the compression function and transmit the raw data at its uncompressed rate in order to prevent loss of data. Accordingly, the main advantage of compressing data, increasing the throughput of the data link, is lost at these higher speeds.
A second technique of compressing data is the use of an external data compression unit, such as the Datamizer, sold by the Symplex Inc., of Ann Arbor, Mich. However, this device is also rate limited at 256 Kbps. Until recently the rate limits of these devices were not significant since most LAN systems were remotely connected at transmission rates of 64 Kbps or less. However, devices such as T1 circuits and CEPT circuits which can provide data at rates much faster have become more inexpensive and accordingly more widely used. T1 circuits provide raw data at a rate up to 1.544 Mbps, while the CEPT circuits provide raw data at a rate of 2.048 Mbps.